Method of producing synthesis gas from a regeneration of spent cracking catalyst

ABSTRACT

The present invention provides a method of producing a synthesis gas from a regeneration of spent cracking catalyst. The method includes introducing a spent cracking catalyst into a first regeneration zone in a presence of a first oxygen and carbon dioxide atmosphere and at a first regeneration temperature. For example, a temperature that does not exceed about 1400° F., and more preferable a temperature that ranges from about 1150° F. to about 1400° F., may be used as the first regeneration temperature. The method further includes introducing the spent cracking catalyst from the first regeneration zone into a second regeneration zone in a presence of a second oxygen and carbon dioxide atmosphere, and producing a synthesis gas from cracking deposits located on the spent cracking catalyst within the second regeneration zone at a second regeneration temperature substantially greater than said first regeneration temperature. In a preferred embodiment, the second regeneration temperature ranges from about 1500° F. to about 1800°, and in a related embodiment is about 1800° F.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to a method of using acatalytic cracker and, more specifically, to a method of producingsynthesis gas from a regeneration of spent cracking catalyst.

BACKGROUND OF THE INVENTION

Catalytic cracking processes have been developed principally forupgrading feed stock derived from natural or synthetic crude oil to morevaluable hydrocarbon mixtures, particularly of lower molecular weight.These lower molecular weight hydrocarbons are generally more desirablebecause of their higher quality and market value. In a typical catalyticcracking process, a crude oil derived feed stock is contacted with ahot, regenerated catalyst, at temperatures ranging from about 1200° F.to about 1400° F. and low to moderate pressures. The chemical reactionsthat take place in the presence of the catalyst include predominantlyscission of carbon-to-carbon bonds (simply cracking), isomerization,polymerization, dehydrogenation, hydrogen transfer, and others,generally leading to lower molecular weight hydrocarbon products.

Some of the cracking reactions in the catalytic cracker also producehydrocarbonaceous compounds of high molecular weight, of very lowvolatility, of very high carbon content and of low combined hydrogencontent. The hydrocarbonaceous compounds tend to be deposited on theactive surfaces of the cracking catalyst and mask the active sites,rendering the catalyst less active, thus unsuitable for continuedcracking without regeneration. Deposits of the hydrocarbonaceous matterand the inclusion of absorbed and adsorbed hydrocarbons, as well as thevaporous combustible components in the fluidizing media between thesolid catalyst particles, collectively called “coke,” are in a senseundesirable. In response to the undesirable buildup of coke on thesurfaces of the catalyst, the oil and gas industry has developed severaltechniques to reduce, or remove, such buildups.

One technique currently used to reduce the coke forming characteristicsof feed stocks, includes without limitation, hydrotreatment,distillation, or extraction of the natural or synthetic crude feed stockprior to charging it to the catalytic cracker. Hydrotreatment,distillation, or extraction of the crude oil derived feed stock servesto remove a substantial amount of the coke precursors, such as containedin asphaltenes, polynuclear aromatics, etc., prior to catalyticcracking. Hydrotreatment, distillation, or extraction are somewhateffective in reducing or removing large amounts of coke precursors fromthe crude oil derived feed stock, however, such processes are expensiveand time-consuming processes. Currently, incrementally available crudeoil is of high residuum content and of higher coke formingcharacteristics at a time when it is unpopular or unlawful to utilizethis additional residuum as fuel oil. At the same time, the market forresiduum products, other than as fuel oil, is saturated. Additionally,to upgrade the residuum materials by the available technology results inproducts of lower quality (and lower market value) than would beachieved by catalytic cracking, provided the coke yield can be handled.Moreover, current and anticipated Federal and State Legislation has, andis, scrutinizing the environmental and storage issues associated withuse, removal or conversion of the coke precursors. Therefore, there is agreat need for an environmentally responsible conversion of the residuumportion of crude oil.

Another technique currently used to remove coke formation from the spentcracking catalyst is to burn the coke away from the catalyst surfaceusing an oxygen-containing gas stream in a separate regenerationreactor. In such a situation, air, oxygen, carbon dioxide, and steam fordiluent as combustion gas, may be introduced into the spent crackingcatalyst in the lower portion of the regeneration zone(s), whilecyclones are provided in the upper portion of the regeneration zone forseparating the combustion gas from the entrained catalyst particles. Thecoke buildup removal process attempts to substantially remove the cokebuildup, and is generally effective, but large amounts of greenhousegases are produced, at least some of which are released into theatmosphere, which is generally environmentally undesirable. Anothertechnique teaches the use of a waste heat boiler as a means of reducinggreenhouse gasses going to the atmosphere, however, the reduction bythis method remains limited to the achievable concentration of a firedheater. U.S. Pat. No. 4,388,218 entitled “Regeneration of CrackingCatalyst in Two Successive Zones” to Rowe, and U.S. Pat. No. 4,331,533entitled “Method and Apparatus for Cracking Residual Oils” to Dean etal., further detail such processes and are included herein by reference.

Similarly, the regeneration zone must be carried out in such a way thatit is in thermal equilibrium with the cracking reaction zone. In otherwords, the sensible heat of the hot regenerated catalyst in thecatalytic cracker should be in balance with the heat requirements of thecatalytic cracking reactor zone. In conventional operations, excludingthe use of internal or external cooling coils for removing heat from theregenerator reaction zone, coke yield of only about 5 to about 8 weightpercent of the total feed may be burned from the catalyst, withoutexceeding the amount of heat required to balance and sustain thecracking reaction.

Thus, to maintain the thermal balance needed to operate the catalyticcracker and remove enough of the coke from the catalyst to sustain thecracking process, one of two things should be done. First, the amount ofcoke that forms on the surface of the catalyst should be reduced.However, as mentioned above, this can typically be accomplished by usinghigher quality feed stock, which is more costly, or subjecting thecurrently available feed stock to the previously mentioned upgrading,such as but not limited to, hydrotreatment, distillation or extractionprocesses, which are also more costly. Second, internal or externalcooling units could be installed in the regeneration units. However,such internal or external cooling units are costly and unreliable.

Accordingly, what is needed in the art is a method of catalyticallycracking crude oil derived feed stock having high coke formingcharacteristics, without experiencing the drawbacks of the prior artmethods.

SUMMARY OF THE INVENTION

To address the above-discussed problems of the prior art, the presentinvention provides a method of producing a synthesis gas from aregeneration of a spent cracking catalyst. The method includesintroducing a spent cracking catalyst into a first regeneration zone ina presence of a first oxygen and carbon dioxide atmosphere and at afirst regeneration temperature. For example, a temperature that does notexceed about 1400° F., and more preferable, a temperature that rangesfrom about 1150° F. to about 1400° F., may be used as the firstregeneration temperature. The method further includes introducing thespent cracking catalyst from the first regeneration zone into a secondregeneration zone. The spent cracking catalyst is introduced into thesecond regeneration zone in a presence of a second oxygen and carbondioxide atmosphere, and at a second regeneration temperaturesubstantially greater than the first regeneration temperature. Asynthesis gas may then be formed from oxidation of the carbon on thecoke located on the spent cracking catalyst within the secondregeneration zone. In a preferred embodiment, the second regenerationtemperature ranges. from about 1500° F. to about 1800° F., and in anexemplary embodiment is about 1800° F.

In contrast to the prior art catalytic cracking method, theabove-mentioned method is capable of producing commercial amounts ofsynthesis gas, which may then be commercially used or sold. Moreover,the above-mentioned method is capable of accepting feed stock havinghigh coke forming characteristics, which in one advantageous embodiment,may be accepted without hydrotreating, separating as a distillationoverhead product, or solvent extracting as an extract product the feedstock prior to catalytic cracking. Both the ability to accept, and theability to accept without the need for hydrotreating, distillation, orsolvent extraction, provide both economical and environmental benefitsnot achieved in the prior art methods.

In another aspect of the invention, the synthesis gas comprises carbonmonoxide. Where the amount of synthesis gas produced is inadequate tomeet the market needs or the intended system consumption capacity, in analternative aspect, a supplemental fuel, such as a hydrocarbonaceousmaterial, may be included within the first or the second combustion gas.The supplemental fuel is preferably one of low hydrogen content and ispreferably introduced into the first regeneration zone. At least aportion of the first oxygen and carbon dioxide atmosphere and the secondoxygen and carbon dioxide atmosphere, may in another aspect, bepreheated to a temperature substantially equal to the first regenerationtemperature and the second regeneration temperature, respectively.

In an alternative embodiment, a carbon dioxide by-product of the firstregeneration zone is used at least as a portion of the second oxygen andcarbon dioxide atmosphere. Likewise, in another embodiment, the secondoxygen and carbon dioxide atmosphere is substantially water-free. Forexample, in an alternative embodiment, the second oxygen and carbondioxide atmosphere has a water content ranging from about 1 to about 10mole percent.

A catalytic cracking process is provided in another aspect of theinvention. The process includes (1) introducing a feed stock and acatalyst into a catalytic cracker, (2) cracking the feed stock into acracked product and coke, the coke forming a deposit on a spent crackingcatalyst, (3) regenerating the spent cracking catalyst obtained from thecatalytic cracker as outlined above, and (4) recycling a regeneratedcatalyst to the catalytic cracker. In an alternative aspect, the feedstock is unseparated feed stock containing asphalt or pitch. However, inanother aspect, the feed stock is a preheated feed stock.

In still another aspect of the present invention, the formation ofsynthesis gas is maximized by (1) utilizing a preheated oxygen andcarbon dioxide atmosphere in both the first and second regenerationzones, (2) avoiding the use of cooling coils in either regenerationzone, therefore oxidizing, in the first reaction zone, only enough cokeand supplemental fuel to oxidize the hydrogen content of the coke andthe supplemental fuel to reduce the water content in the secondregeneration zone so as to avoid exceeding the operating conditionswhich result in destroying the cracking catalyst. Such conditions are afunction of the second regeneration zone temperature and flue gas watercontent.

The foregoing has outlined, rather broadly, preferred and alternativefeatures of the present invention so that those skilled in the art maybetter understand the detailed description of the invention thatfollows. Additional features of the invention will be describedhereinafter that form the subject of the claims of the invention. Thoseskilled in the art should appreciate that they can readily use thedisclosed conception and specific embodiment as a basis for designing ormodifying other structures for carrying out the same purposes of thepresent invention. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

FIG. 1 illustrates one embodiment of a catalytic cracking system whereinthe inventive method may be practiced.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is a schematic diagram of anexemplary configuration of a catalytic cracking system 100. In theillustrative embodiment shown in FIG. 1, the catalytic cracking system100 includes a catalytic cracking reaction zone 200, a firstregeneration zone 300, and a second regeneration zone 400. Those skilledin the art will understand that the first regeneration zone 300 or thesecond regeneration zone 400 may include a contact system other than thedilute phase (entrained) flow section as shown in FIG. 1, there beingother regeneration zone designs suitable for use with the disclosedinvention. Likewise, those skilled in the art will also understand thatthe present invention is not limited to a single cracking reaction zone200 and two regeneration zones 300, 400, and that multiple crackingreaction zones and regeneration zones are within the scope of thepresent invention. It should also be noted that valves, flanges,fittings, and some associated pumps, exchangers, and instruments may notbe shown in FIG. 1 for simplicity reasons.

In the illustrative embodiment shown in FIG. 1, the catalytic crackingreaction zone 200 includes a cracker reactor disengaging space 210, aspent catalyst steam stripper 220, a dilute phase cracking reactortransport line 230 and a cracked product exit line 240. The catalyticcracking reaction zone 200 may also, in an exemplary embodiment, includecyclones 250. In the embodiment shown in FIG. 1 the cyclones 250 areshown as a single cyclone, however, it should be noted that there may bemore than one cyclone in parallel, or even groups of cyclones in seriesor in series and in parallel. It should be noted that the cyclones forthe catalytic cracking reaction zone 200, the first regeneration zone300, or the second regeneration zone 400, shown as internal cyclones,may be externally mounted without changing the teaching of thisdisclosed invention. The catalytic cracking reaction zone 200 in theembodiment shown in FIG. 1 is a dilute phase fluid bed catalyticcracker, but those skilled in the art understand that the fluid bedcatalytic cracker may be replaced with a moving bed catalytic cracker,falling bed catalytic cracker or fixed bed catalytic cracker, withoutdeparting from the scope of the present invention.

In the illustrative embodiment shown in FIG. 1, the first regenerationzone 300 includes a first disengaging space 310, a partially regeneratedcatalyst line 320, a first regenerator dilute phase transport line 330and a first regeneration zone flue gas line 340. Similar to thecatalytic cracking reaction zone 200, the first regeneration zone 300may, in a preferred embodiment, include cyclones 350. In the embodimentshown in FIG. 1, two cyclones 350 are shown in series, however, itshould be noted that one or more cyclones, in series, parallel, or both,are also within the scope of the present invention. The firstregeneration zone 300 may also include a first regeneration zonetreating or separation system 360. Any one or combination of knowntreating or separation processes may be used, for example withoutlimitation, removal of water, sulfur oxide (SO_(X)), nitrogen oxide(NO_(X)) and carbon monoxide (CO).

In the illustrative embodiment shown in FIG. 1, the second regenerationzone 400 includes a second disengaging space 410, a regenerated catalystline 420, a second regenerator dilute phase transport line 430, and asecond regeneration zone flue gas line 440. Similar to the catalyticcracking reaction zone 200, the second regeneration zone 400 may, in apreferred embodiment, includes cyclones 450. In the embodiment shown inFIG. 1 two cyclones 450 are shown in series, however, it should be notedthat one or more cyclones, either in series, in parallel, or both, arewithin the scope of the present invention. The second regeneration zone400 may also include a second regeneration zone treating or separationsystem 460. Those skilled in the art will realize that other types ofcatalytic cracking system 100 designs may satisfy the requirements ofthe present invention without changing the teachings disclosed herein,including using multiple reaction zones, instead of the first and secondregeneration zones 300, 400, illustrated in FIG. 1.

It has been found that typical oxidizing reactions proceed more rapidlyat higher temperatures. However, it has also been found that eachindividual oxidizing reaction rate disproportionately changes withtemperature. To understand such a process, the following oxidizingreactions have been provided:

(1) C+½O₂=CO;

(2) C+O₂=CO₂;

(3) C+CO₂=2CO;

(4) C+H₂O=CO+H₂; and

(5) C+2H₂O=CO₂+2H₂.

It has been found that the reaction rate (change in a reactantsconcentration as a function of time) for reaction 1 increases morerapidly with increased temperature than does reaction 2. At temperaturesbelow 1400° F. the equilibrium molal ratio of CO/CO₂ is well belowunity, where at temperatures near 1800° F. the CO/CO₂ molal ratio ismuch greater. By limiting oxygen input such that there is little or noexcess oxygen at temperatures ranging between the cracking reactortemperature and about 1400° F. the formation of CO₂ is favored. Attemperatures between about 1400° F. and about 1800° F. the formation ofCO is favored and the oxidization is rapid.

It has also been found, that even the most thermally stable crackingcatalyst commercially used is stable up to a temperature of about 1400°F., in the presence of the water vapor content normally experienced inregenerating said cracking catalyst. Furthermore, it has been found thatsuch commercially used cracking catalyst may be subjected totemperatures up to about 1800° F. in contact with oxidizing gas (fluegas) of decreased water content, the allowable water content beingsomewhat inversely proportional to temperature.

It is further known that the reaction rate of reaction 3 is almostnonexistent at or below temperatures of about 1400° F., but becomessignificant between about 1400° F. and about 1800° F. From these facts,it has been found that the most favorable method of regeneratingcracking catalyst to produce carbon monoxide (CO) is to first oxidizeonly enough of the coke as to reduce the concentration of combinedhydrogen in the coke, the hydrogen compounds being more rapidly oxidizedthan virtually all the carbon compounds, especially the elementalhydrogen or low molecular weight fuel, such as but not limited tomethane. After having reduced the combined hydrogen content of the cokein the first regeneration zone 300, the remainder of the carbon of thecoke in a second regeneration zone 400, may be oxidized at a highertemperature without damage to the catalyst.

The discussion will now turn to specific details of a method of usingthe catalytic cracking system 100, or another similar system, to producea commercial amount of a synthesis gas while regenerating a spentcracking catalyst. Initially a feed stock 510 is supplied to a lowerportion of the dilute phase cracking reactor transport line 230 where itis combined with regenerated catalyst provided from the regeneratedcatalyst line 420. The feed stock 510, in an exemplary embodiment,comprises a fresh feed stream combined with a recycled hydrocarbonstream and a specified amount of steam. Moreover, prior to entering thelower portion of the dilute phase cracking reactor transport line 230,the feed stock 510 may be preheated in a furnace 520. The furnace 520may provide for a controlled increase in the temperature of the feedstock 510, or vaporization of at least a part thereof, which mayfacilitate the reaction between the feed stock 510 and the regeneratedcatalyst provided from the regenerated catalyst line 420. It should benoted, and is well understood by one skilled in the art, that the feedstock 510 flowing through the furnace 520 for preheating, may include atleast portions of recycled hydrocarbon stream and steam through pipingnot shown, and that the feed stock 510 could include other similarmaterials. In one particularly advantageous embodiment, the fresh feedstream comprises a high coke forming feed stock, such as an unseparatedfeed stock containing high amounts of asphalt and pitch. As previouslymentioned, the feed stock may be preheated in the furnace 520, however,in an alternative embodiment, the feed stock 510 may be bypassed aroundthe furnace 520, using lines not shown herein.

After entering the lower portion of the dilute phase cracking reactortransport line 230 and combining with the regenerated catalyst from theregenerated catalyst line 420, the hydrocarbons react to form reactants,and the mixture rises to the upper portion of the dilute phase crackingreactor transport line 230. The mixture may then discharge from theupper portion of the dilute phase cracking reactor transport line 230into the cracking reactor disengaging space 210, where crackingreactions continue. As is understood by one skilled in the art, thecracking process produces vaporous cracked material and spends crackingcatalyst by depositing coke thereon. Once within the cracking reactordisengaging space 210, vaporous cracked material rises to the upperportion of the cracking reactor disengaging space 210. In a preferredembodiment, the vaporous cracked material rises to the upper portion ofthe cracking reactor disengaging space 210 and enters one or a pluralityof the cyclones 250. The cyclones 250 tend to separate the vaporouscracked material from any remaining spent catalyst suspended therein.The vaporous cracked material may then rise and exit through the crackedproduct exit line 240 and then flow to separation equipment (not shown).The spent catalyst removed by the cyclones 250 may then flow downwardlyand discharge from a dip leg of the cyclones 250.

The spent catalyst may then flow from the lower portion of the crackingreactor disengaging space 210 to the spent catalyst steam stripper 220.In the illustrative example shown in FIG. 1, the spent catalyst flowsdownwardly as steam countercurrently flows upwardly. The steam may beprovided using a steam input line 530, and alternatively may besuperheated, up to a temperature of about 1400° F., prior to enteringthe steam stripper 220. Depending on the design of the catalyticcracking system 100, the upward flowing steam may flow from the steamstripper 220 to the lower portion of the cracker reactor disengagingspace 210, or the upward flowing steam may alternatively be withdrawnusing a steam seal, piping and valve that is not shown.

Spent and steam stripped, the spent cracking catalyst may flow from thecatalyst cracking reaction zone 200, through a carrier line 540, to thefirst regeneration zone 300. In a more specific example, the spentcracking catalyst may enter the lower portion of the first regeneratordilute phase transport line 330. At the lower portion of the firstregenerator dilute phase transport line 330, the spent cracking catalystis introduced to a first oxygen and carbon dioxide atmosphere. In apreferred embodiment, the first oxygen and carbon dioxide atmospherecomprises a first combustion gas. As used herein, oxygen includescommercially available pure, or internally produced pure oxygen. As alsoused herein, the carbon dioxide atmosphere includes a carbon dioxiderich atmosphere. Preferably, the carbon dioxide rich atmospherecomprises in excess of about 50 mole percent carbon dioxide, and evenmore preferably, in excess of about 75 mole percent carbon dioxide. Itshould be noted, however, that the present invention is not limited tosuch percentages.

In a preferred embodiment, the first oxygen and carbon dioxideatmosphere or the carbon dioxide portion of the atmosphere, may bepreheated in a furnace 550 prior to combining with the spent crackingcatalyst. In another preferred embodiment, the furnace 550 preheats thefirst oxygen and carbon dioxide atmosphere to a temperaturesubstantially equal to the operating temperature of the firstregeneration zone 300. The components of the first oxygen and carbondioxide atmosphere are shown in FIG. 1 as flowing into a common lineprior to entering the lower portion of the first regenerator dilutephase transport line 330, however, the skilled artisan will understandthat any one or any portion of these flows may be introduced throughfurnace 550 separately or in combination.

The amount of the first oxygen and carbon dioxide atmosphere may vary,however, the amount of each gas component should be adjusted so as tooxidize a minimal portion of the net coke, but to reduce the hydrogencontent of the coke on the surface of the spent cracking catalystleaving the first regeneration zone 300. In one advantageous embodiment,the amount of each gas component should be controlled to achieve a firstregeneration zone 300 temperature not to exceed about 1400° F., and moreprecisely, a first regeneration zone 300 temperature ranging from about1150° F. to about 1400° F. Cracking temperatures above about 1400° F.,in the presence of anticipated water concentration, like provided in thefirst regeneration zone 300, are generally undesirable since they tendto cause damage to the cracking catalyst.

The spent cracking catalyst and the first oxygen and carbon dioxideatmosphere flow upwardly within the first regenerator dilute phasetransport line 330 to the first disengaging space 310 for separation ofvaporous reactants from the spent catalyst. Partially regeneratedcatalyst flowing from the upper portion of the first regenerator dilutephase transport line 330 tends to fall into the lower portion of thefirst disengaging space 310 to form a fluid bed. While located withinthe fluid bed, additional oxidation of the coke from the partiallyregenerated catalyst may occur. To facilitate the additional oxidationwithin the fluid bed, in an exemplary embodiment, additional amounts ofoxygen and carbon dioxide atmosphere may be introduced within the fluidbed. For example, the additional amounts of oxygen and carbon dioxideatmosphere may be introduced within the fluid bed through a distributiongrid or piping coil.

The vaporous reactants of the first regeneration zone 300 tend to risewithin the first disengaging space 310 and enter cyclones 350. Thecyclones 350, similar to the cyclones 250 found within the catalyticcracking reaction zone 200, may separate suspended spent catalyst fromthe vaporous reactant's flue gas. Spent catalyst removed from thevaporous flue gas flows downwardly through the dip leg to the fluid bed,as the vaporous flue gas exits the first regeneration zone 300 throughthe first regeneration zone residue gas line 340. In one advantageousembodiment, the vaporous flue gas then enters the first regenerationzone treating or separation system 360. The vaporous flue gas may begiven treatment or separation utilizing any one or more of several typesof well-known treatments. Such treatments or separation may separate thevaporous flue gas into its constituent components consistent with itsintended use. At temperatures ranging from about 1150° F. to about 1400°F., the most rapid compounds to oxidize are those which containhydrogen, sulfur and nitrogen, however, carbon dioxide, carbon monoxideand other pollutants are also present in the flue gas. In oneparticularly advantageous embodiment, the carbon dioxide flue gasby-product of the first regeneration zone 300 provides the carbondioxide needed in the first regeneration zone 300.

A portion of the hot partially regenerated spent catalyst located withinthe fluid bed may be recycled through a line 560 to the lower portion ofthe first regenerator dilute phase transport line 330. This may be usedto accelerate the initial oxidizing reaction rate in the firstregenerator dilute phase transport line 330. However, the remainingportion of the partially regenerated spent catalyst travels through apartially regenerated catalyst line 320 to the second regeneration zone400. In a preferred embodiment, the remaining portion of the partiallyregenerated spent catalyst travels through the partially regeneratedcatalyst line 320 to a lower portion of the second regenerator dilutephase transport line 430.

At the lower portion of the second regenerator dilute phase transportline 430, the partially regenerated spent cracking catalyst from thefirst catalyst transport line 320 is introduced to a second oxygen andcarbon dioxide atmosphere. In a preferred embodiment, the second oxygenand carbon dioxide atmosphere comprises a combustion gas. The partiallyregenerated spent cracking catalyst and the second oxygen and carbondioxide atmosphere, in an exemplary embodiment, are substantiallywater-free. For example, in another exemplary embodiment, flue gas fromthe regeneration of the partially regenerated spent cracking catalystalong with the second oxygen and carbon dioxide atmosphere, have a watercontent ranging from about 1 to about 10 mole percent.

In one particularly advantageous embodiment, the carbon dioxide flue gasby-product of the first regeneration zone 300 provides the carbondioxide needed in the second regeneration zone 400. In a preferredembodiment, the second oxygen and carbon dioxide atmosphere, or strictlythe carbon dioxide portion of the atmosphere, may be preheated in afurnace 570 prior to combining with the oxygen and the spent crackingcatalyst. Similar to the furnace 550, the furnace 570 may preheat thesecond oxygen and carbon dioxide atmosphere, or strictly the carbondioxide portion of the atmosphere, to a temperature substantially equalto the operating temperature of the second regeneration zone 400. Thoseskilled in the art will also realize that the preheating of the secondoxygen and carbon dioxide atmosphere, or strictly the carbon dioxideportion of the atmosphere, may also be accomplished by heat exchangewith a hot process stream. The hot process stream, in an exemplaryembodiment, could include the first regeneration zone flue gas line 340or the second regeneration zone flue gas line 440. The second oxygen andcarbon dioxide atmosphere is preferably preheated, because it has beenfound that the carbon dioxide will begin to react with the carbon on thecoke endothermically to form more carbon monoxide at a decreasingtemperature, thus limiting the second reactor temperature in the secondregeneration zone 400. The components of the second oxygen and carbondioxide atmosphere are shown in FIG. 1 as flowing into a common lineprior to entering the lower portion of the second regenerator dilutephase transport line 430, however the skilled artisan will understandthat any one or a portion of these flows may be introduced separately orin combination.

The flow rate of each component of the second oxygen and carbon dioxideatmosphere introduced to the second regeneration zone may vary, however,the flow rate of each component should be adjusted independently so asto oxidize the remaining net coke production, yet operate in a partialoxidizing mode. In one advantageous embodiment, the amount of eachcomponent should be controlled individually to achieve a secondregeneration zone 400 temperature substantially greater than the firstregeneration zone 300 temperature, and to achieve optimum conversion ofthe coke and supplemental fuel to carbon monoxide. For example, thesecond regeneration zone 400 temperature may range from about 1500° F.to about 1800° F., and more precisely, may have a temperature of about1800° F. Since the water forming hydrogen content of the coke wassubstantially reduced in the first regeneration zone 300, the partiallyregenerated spent cracking catalyst can handle temperatures up to about1800° F. without damage, which is contrary to the first regenerationzone 300, and contrary to the prior art carbon monoxide (synthesis gas)forming regenerators. Generally, the heat generated in the secondreaction zone 400 is desirable for the reaction and should remaintherein. For example, in a preferred embodiment, the first and secondregeneration zones 300, 400, respectively, should not have a significantamount of heat removed, because to do so could suppress the endothermicreaction of carbon dioxide with carbon, to form additional carbonmonoxide and reduce the cost of oxygen requirements. Thus, those skilledin the art now understand the use of carbon dioxide to minimize thecostly oxygen requirement and to maximize the production of carbonmonoxide.

The partially regenerated spent cracking catalyst and the second oxygenand carbon dioxide atmosphere flow upwardly within the secondregenerator dilute phase transport line 430 to the second disengagingspace 410 for separation of the remaining coke from the partiallyregenerated spent catalyst. Partially regenerated catalyst flowing fromthe upper portion of the second regenerator dilute phase transport line430 tends to fall into the lower portion of the second disengaging space410 to form a fluid bed. While located within the fluid bed, additionaloxidation of the coke from the partially regenerated catalyst may occur.To facilitate the additional oxidation within the fluid bed, in anexemplary embodiment, additional carbon dioxide and oxygen may beintroduced within the fluid bed. For example, the additional carbondioxide and oxygen atmosphere may be introduced within the fluid bed ata point below a distribution grid or piping coil.

The vaporous reactants of the second regeneration zone 400 tend to risewithin the second disengaging space 410 and enter the cyclones 450. Thecyclones 450, similar to the cyclones 250 found within the catalyticcracking reaction zone 200, may separate suspended spent catalyst fromthe vaporous flue gas. Spent catalyst removed from the vaporous flue gasmay then flow downwardly through the dip leg to the fluid bed, as thevaporous flue gas exits the second regeneration zone 400 through thesecond regeneration flue gas line 440. The vaporous flue gas may thenenter the second regeneration zone treating or separation system 460.The vaporous flue gas may be given treatment or separation utilizing anyone or more of several types of well-known treatments or separations.Such treatments may separate the vaporous flue gas into its constituentcomponents. In contrast to the first regeneration zone 300 where largeamounts of carbon dioxide are formed, the second regeneration zone 400produces larger amounts of synthesis gas, such as carbon monoxide. Thisis a result of the higher temperatures used in the second regenerationzone 400 favoring the formation of carbon monoxide rather than carbondioxide. Other minor constituents produced by the treatment of thevaporous flue gas include water, sulfur compounds, nitrogen compounds,carbon dioxide and particulate matter. It should be pointed out, incontrast to the prior art systems, that it has been found that the useof cooling coils within either the first or second regeneration zones300, 400, simply reduces the efficiency of the first or secondregeneration zones 300, 400, to maximize the production of carbonmonoxide. For such a reason, it is preferred that cooling coils not beused within either the first or second regeneration zones 300, 400.

In one particularly advantageous embodiment, high enough amounts ofcarbon monoxide are produced from the coke and alternativelysupplemental fuels, if any, to fuel or feed other systems within thepetrochemical plant, or be sold to an external enterprise. Regardless,using the above-mentioned process has turned what was historicallyconsidered waste into a valuable and profitable resource. In situationswhere the operator of the catalytic cracking system 100 has entered intoan agreement with an external enterprise to provide a specified amountof carbon monoxide, and the coke forming characteristics of the feedstock are not great enough to provide the agreed upon quantity of carbonmonoxide or hydrogen gas, supplemental fuel 575 may be included with thefirst or second oxygen and carbon dioxide atmospheres, or addedseparately. Although the supplemental fuel 575 may be added to the firstor the second regeneration zone, it is preferred to add it to the firstregeneration zone so as to reduce the hydrogen content, if any, of suchfuel 575 components before the carbon content thereof flows to thesecond regeneration zone operated at temperatures at which the catalystmay be damaged by water content. Inclusion of the supplemental fuel 575helps to increase the output of the carbon monoxide. For instance, aspecified amount of a carbon-based material highly deficient in hydrogencould be supplemented with the first or second oxygen and carbon dioxideatmosphere, or added separately. Such carbon-based materials may includecarbon derived from coal, pitch, and many others. Furthermore, it ispreferred to use a high carbon-based material having low concentrationsof hydrogen, ash, and sulfur.

It should be noted that carbon monoxide may not be the only flue gasconstituent produced in high enough quantities for resale. In apreferred embodiment of the invention, carbon dioxide flue gas byproductproduced from the first regeneration zone 300, and carbon dioxide fluegas by-product produced from the second regeneration zone 400, isproduced in a quantity sufficient to provide the carbon dioxideatmospheres needed in the first and second regeneration zones 300, 400,and also provide an additional quantity of carbon dioxide sufficient forresale.

Once the vaporous flue gas has been separated from the substantiallyregenerated catalyst, a portion of the hot substantially regeneratedcatalyst located within the fluid bed may be recycled through a line 580to the lower portion of the second regenerator cracking reactor dilutephase transport line 430, to increase the initial temperature therein.However, the remaining portion of the substantially regenerated catalystmay then flow through the second regenerated catalyst transport line 420to the lower portion of the dilute phase cracking reactor transport line230. The substantially regenerated catalyst then recombines with thefeed stock as previously mentioned, and the process repeats itself. Inan exemplary embodiment, located in the second regenerated catalysttransport line 420, between the second regeneration zone 400 and thecatalyst cracking reaction zone 200, may be a heat exchanger 590. Theheat exchanger 590, which in a preferred embodiment cools thetemperature of the regenerated catalyst to a desired temperature, andattempts to adjust the catalyst to oil weight ratio (C/O) for increasedcracking selectivity. This temperature may range from about 1150° F. toabout 1500° F. In FIG. 1, the preheaters 520, 550, and 570 are shown asfired heaters, but those skilled in the art will realize that thepreheating may be at least in part accomplished by heat exchange suchas, but not limited to, exchanger 590, without changing the teaching ofthis disclosed invention.

The above mentioned inventive method of producing a synthesis gas fromregeneration of a spent cracking catalyst has many monetary andenvironmental benefits associated therewith. Of particular importance isthe ability of the current inventive method to convert the vaporous fluegas, which was historically considered waste, into usable andnon-environmentally objectionable material. Historically, the vaporousflue gas was passed through a waste heat boiler, treated, for examplefor reduction of sulfur compounds or particulate matter, and releasedinto the atmosphere, all the while raising environmental concerns.However, since the current process is capable of producing commercialamounts of synthesis gas, and that synthesis gas is captured, the amountof particulate matter (PM), sulfur oxide (SO_(X)), nitrogen oxide(NO_(X)) and volatile organic compounds (VOC) released into theatmosphere by the second regeneration zone 400 is substantially reduced.Moreover, not only are these emissions reduced, but they are reduced bypurification of product synthesis gas.

Another environmental and monetary benefit resulting from the inventivemethod of producing a synthesis gas from regeneration of a spentcracking catalyst, resides in the ability of the catalytic cracker 100to accept heavier feed stock (long residuum), i.e., feed stockscontaining high amounts of asphalt, pitch and other high coke formingconstituents, without the need to hydrotreat, distill, or extract suchfeed stocks prior to catalytic cracking. However, this is not to saythat the hydrotreatment may not still be profitable. Currently, thequality of the crude oil derived feed stock has decreased in recentyears, and unless one is willing to pay a very high premium to get veryhigh quality feed stock, heavy feed stock was the only option. However,as a result of the above-mentioned process, the use of heavy feed stockis now a plausible option.

Historically, using the heavy feed stock required distilling,extracting, or hydrotreating of the long residuum, asphalt, pitch andother components of high coke forming characteristic feed stock, priorto catalytically cracking such a feed stock. However, since thedistillation process may be dispensed with for many crude oil sources,environmental and storage concerns associated with the removal of theasphalt, pitch and other high coke forming constituents aresubstantially reduced. Likewise, any emissions into the atmosphereresulting from the hydrotreating, distillation or extraction processesare substantially reduced. Therefore, the ability to accept raw heavyfeed stock is both environmentally and momentarily beneficial.

Some reduction in the emissions from sources other than the catalyticcracker may also be realized. Such possible sources may include, inaddition to hydrotreatment, distillation, and extraction processingequipment, the alternate conversion equipment, such as but not limitedto, coker processing equipment. Because the amount of long residuumwhich is processed in such sources is substantially reduced oreliminated, the emissions of such sources would be reduced accordingly.Emissions such as fugitive emissions are generally unaffected unless thetotal operation is discontinued.

Another benefit realized by the inventive method, and more specificallythe higher production rate of synthesis gas, is that only about 28% ofthe heat evolved in complete combustion mode of regeneration isexperienced in forming carbon monoxide in the catalyst regenerators. Thelower heat output plays an important factor in maintaining the catalyticcracking system in thermal equilibrium, while continuing to removeenough of the coke from the catalyst to sustain the cracking process.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form. For example, thoseskilled in the art will understand that there are almost limitless waysthat the process of FIG. 1 can be modified without departing from theteachings of the herein described invention.

What is claimed is:
 1. A method of producing a synthesis gas productfrom a regeneration of spent cracking catalyst, comprising: introducinga spent cracking catalyst into a first regeneration zone in a presenceof a first oxygen and carbon dioxide atmosphere, wherein said firstregeneration zone is operated at a temperature ranging from about 1150°F. to about 1400° F. so as to reduce cracking catalyst damage resultingfrom high temperature regeneration with a high moisture contentatmosphere, and so as to oxidize a greater amount of a hydrogen contentthan carbon content of coke associated with said spent crackingcatalyst, thereby substantially reducing a water content of a subsequentregeneration zone, and wherein said carbon dioxide of said first oxygenand carbon dioxide atmosphere is a diluent for said oxygen of said firstoxygen and carbon dioxide atmosphere; and introducing said spentcracking catalyst from said first regeneration zone into a secondregeneration zone in a presence of a second oxygen and carbon dioxideatmosphere, wherein said second regeneration zone is operated at atemperature ranging from about 1500° F. to about 1800° F. and maintainedin a partial oxidation mode, said second regeneration zone temperatureand partial oxidation mode of operation causing a substantial portion ofsaid carbon dioxide of said second oxygen and carbon dioxide atmosphereto function as a reactant with carbon remaining associated with saidspent cracking catalyst to form two moles of carbon monoxide per mole ofcarbon dioxide reacted, and thus result in a synthesis gas product richin carbon monoxide.
 2. The method as recited in claim 1 wherein saidfirst or said second oxygen and carbon dioxide atmosphere furtherincludes a supplemental fuel.
 3. The method as recited in claim 2wherein said supplemental fuel is a hydrocarbonaceous material.
 4. Themethod as recited in claim 1 wherein at least a portion of said firstoxygen and carbon dioxide atmosphere is preheated to a temperaturesubstantially equal to said first regeneration temperature.
 5. Themethod as recited in claim 1 wherein at least a portion of said secondoxygen and carbon dioxide atmosphere is preheated to a temperaturesubstantially equal to said second regeneration temperature.
 6. Themethod as recited in claim 1 wherein introducing a spent crackingcatalyst into a first regeneration zone includes forming a carbondioxide by-product.
 7. The method as recited in claim 6 wherein saidcarbon dioxide by-product forms a part of said second oxygen and carbondioxide atmosphere.
 8. The method as recited in claim 1 wherein saidsecond oxygen and carbon dioxide atmosphere is substantially water-free.9. The method as recited in claim 8 wherein said second oxygen andcarbon dioxide atmosphere has a water content ranging from about 1 toabout 10 mole percent.
 10. The method as recited in claim 1 wherein saidcarbon dioxide of said second oxygen and carbon dioxide atmosphere alsofunctions as a diluent for said oxygen of said second oxygen and carbondioxide atmosphere.
 11. A catalytic cracking process, comprising:introducing a feed stock and a catalyst into a catalytic crackerreaction zone; cracking said feed stock into a cracked product and aspent cracking catalyst; regenerating said spent cracking catalystobtained from said catalytic cracker reaction zone, including;introducing said spent cracking catalyst from said catalytic crackerreaction zone into a first regeneration zone in a presence of a firstoxygen and carbon dioxide atmosphere, wherein said first regenerationzone is operated at a temperature ranging from about 1110° F. to about1400° F. so as to reduce cracking catalyst damage resulting from hightemperature regeneration with a high moisture content atmosphere, and soas to oxidize a greater amount of a hydrogen content than carbon contentof coke associated with said spent cracking catalyst, therebysubstantially reducing a water content of a subsequent regenerationzone, and wherein said carbon dioxide of said first oxygen and carbondioxide atmosphere is a diluent for said oxygen of said first oxygen andcarbon dioxide atmosphere; and introducing said spent cracking catalystfrom said first regeneration zone into a second regeneration zone in apresence of a second oxygen and carbon dioxide atmosphere, wherein saidsecond regeneration zone is operated at a temperature ranging from about1100° F. to about 1800° F. and maintained in a partial oxidation mode,said second regeneration zone temperature and partial oxidation mode ofoperation causing a substantial portion of said carbon dioxide of saidsecond oxygen and carbon dioxide atmosphere to function as a reactantwith carbon remaining associated with said spent cracking catalyst toform two moles of carbon monoxide per mole of carbon dioxide reacted,and thus result in a synthesis gas product rich in carbon monoxide; andrecycling a regenerated catalyst from said second regeneration zone tosaid catalytic cracker reaction zone.
 12. The process as recited inclaim 11 wherein introducing a feed stock includes introducing anunseparated feed stock.
 13. The process as recited in claim 12 whereinintroducing an unseparated feed stock includes introducing anunseparated feed stock containing asphalt or pitch.
 14. The process asrecited in claim 11 wherein said first or said second oxygen and carbondioxide atmosphere further includes a supplemental fuel.
 15. The processas recited in claim 14 wherein said supplemental fuel is ahydrocarbonaceous material.
 16. The process as recited in claim 11wherein at least a portion of said first oxygen and carbon dioxideatmosphere is preheated to a temperature substantially equal to saidfirst regeneration temperature.
 17. The process as recited in claim 11wherein at least a portion of said second oxygen and carbon dioxideatmosphere is preheated to a temperature substantially equal to saidsecond regeneration temperature.
 18. The process as recited in claim 11wherein introducing a spent cracking catalyst into a first regenerationzone includes forming a carbon dioxide stream by-product.
 19. Theprocess as recited in claim 18 wherein the carbon dioxide streamby-product forms a part of said second oxygen and carbon dioxideatmosphere.
 20. The process as recited in claim 11 wherein said secondoxygen and carbon dioxide atmosphere is substantially water-free. 21.The process as recited in claim 20 wherein said second oxygen and carbondioxide atmosphere has a water content ranging from about 1 to about 10mole percent.
 22. The catalytic cracking process as recited in claim 11wherein said carbon dioxide of said second oxygen and carbon dioxideatmosphere also functions as a diluent for said oxygen of said secondoxygen and carbon dioxide atmosphere.